Relative-rotational-position detection apparatus

A relative-rotational-position detection apparatus for detecting a relative rotational position between a first shaft and a second shaft rotatable relative to each other, which comprises:

• an outer cylindrical section rotatable with said first shaft, said outer cylindrical having a nonmagnetic and nonconductive cylindrical base and magnetic shielding portions that are formed of a magnetic shielding or antimagnetic substance and arranged on a surface of the cylindrical base, the magnetic shielding portions being spaced apart from each other by a predetermined interval in a circumferential direction of the cylindrical base so that non-magnetically-shielding portions are formed between the magnetic shielding portions;
• a plurality of coils provided on a periphery of said outer cylindrical section and excitable by a predetermined A.C. signal;
• and
• an inner cylindrical section inserted in said outer cylindrical section and rotatable with said second shaft, said inner cylindrical section including magnetic portions each provided to present a different characteristic with respect to an arrangement of said plurality of coils;
• wherein a degree of overlap between the non-magnetically-shielding portions of said outer cylindrical section and the magnetic portions of said inner cylindrical section varies in response to a variation in a relative rotational position between said first shaft and said second shaft, each of said coils presenting a different impedance corresponding to said degree of overlap.